1. Field of the Invention
The present invention is concerned with a system for resolving atherosclerotic plaque build-up in vivo. More particularly, the invention hereof involves a hot tip catheter assembly and technique for temperature control removal of arterial plaque.
2. Description of the Prior Art
Coronary artery disease occurs when arteries which supply oxygen-rich blood to the heart are narrowed (partially blocked) by a build up of fatty and fibrous substances known as atherosclerotic plaque. Arteries are composed of three layers. The innermost layer is the intima, the middle layer is the muscularis, and the outermost layer is the adventitia. The atherosclerotic plaque is deposited directly underneath the intima. The plaque can build up on coronary as well as peripheral arteries.
Various conventional methods are currently used for opening arteries which are constricted by atherosclerotic plaque, and several accomplish this by compression or removal of the plaque which results in residual sites of injury which predisposes to recurrent occlusion. These methods are generally seen as alternatives to coronary artery bypass procedures which are expensive and traumatic in terms of patient morbidity. One of the most commonly used methods is percutaneous transluminal balloon dilatation (angioplasty) which reduces the blockage by dilatation of the lumen of the artery, which reforms and compresses atherosclerotic plaque. Another method is the use of implantable stents in cases where the arteries have failed to remain patent after balloon angioplasty. Atherectomy devices are used to physically cut through the atherosclerotic plaque and remove it from the artery. Laser angioplasty is also available wherein a channel is created through the arteries by heating or melting the plaque using a laser. Other non-laser devices have been developed which also soften or melt plaque using various thermal means.
Balloon angioplasty is not always effective, however, especially when the plaque has hardened due to the presence of a high concentration of calcium in the plaque. Further, if the lumen of the artery is mostly or completely constricted, balloon angioplasty is not feasible as the balloon catheter cannot be placed within the opening of the blockage.
The angioplasty devices which are currently used to soften or melt the atherosclerotic plaque have several drawbacks. These devices often cause damage to the interior walls of the arteries by misdirecting the thermal energy used, focusing it on the arterial wall rather than the plaque. Damage can also be caused by a failure to accurately and effectively regulate and maintain the temperature of the thermal energy used. If the temperature gets too high, a hole can be burned through the wall of the artery. No effective system for precisely regulating temperature at the tip of a thermal ablating device are available.
Furthermore, conventional thermal devices often have problems being cooled by the surrounding tissue with sufficient speed, generally due to the relatively high thermal mass of the catheters. Current leakage has been another problem with prior thermal devices, which may result in lethal cardiac arrhythmias. An additional problem with prior thermal devices is the formation of char from themally damaged debris on the top of the heated cap, which may cause adhesion of the catheter tip to the vessel wall.